174 [September, 



tinguished from the latter by the presence of much larger scales, and especially 

 upon the dorsal region, where they are very small in A. latijnnnis. 



D 13 ; A t ; C 4, 1, 8, 8, 1, 4 ; V 9 ; P 17. 



The anterior two rays, in both the dorsal and anal, are rudimentary ; so also 

 the exterior one in the ventrals. 



The head forms the fifth of its total length ; the shape is subquadrangnlar, 

 subpyramidal. The eyes are small and circular. The lips are well developed 

 and covered with large papillae, but the posterior one is less indented than in 

 A. latipinnis. 



The upper regions are purplish black, with an orange lateral band from head 

 to tail. The inferior regions are yellowish white. 



Si^ecimens of this species were collected by Dr. C. B. Kennerly, under Major 

 Emory, in Janos River, which empties its water in Guzman Lake, State of Chi- 

 huahua. 



5. Catostomus ( Acomus) generosus. It is a rather short and contracted species, 

 particularly when compared to A. griseus. The head constitutes about the fifth 

 of the total length. The eye is moderate in size and circular. The anterior 

 margin of the dorsal fin is equi-distant between the tip of the snout and the in- 

 sertion of the caudal fin. The scales are larger than in A. griseus. The dorsal 

 region, as well as the flanks, are olivaceous brown, spotted with black. Inferiorly 

 unicolor. 



Specimens were collected in Cottonwood Creek, an affluent of the great Salt 

 Lake of Utah, and brought home by Lieut. E. G. Beckwith, U. S. A. 



6. Catostomus (Acomus) griseus. The body is slender, gracefully fusiform 

 iu its outline, the head forming the fifth of the entire length. The anterior 

 margin of the dorsal is equidistant between the tip of the snout and the inser- 

 tion of the caudal fin. Tlae ventrals are inserted opposite the posterior third of 

 the dorsal. The anal is slender. 



D 13 ; A 10 ; C 6, 1, 8, 8, 1, 5 ; V 10 ; P 16. 



Collected in the Sweet Water fork of Platte River, by J. S. Bowman, Esq. 

 Scales exhibiting radiating furrows all around. Upper regions greyish ; infe- 

 rior regions whitish or yellowish. 



7. Catostomus (Acomus) lactarius is closely allied to the preceding species, 

 from which it differs by a stouter head and larger eyes, and larger scales on the 

 body. The structure of the scales themselves is very different, since the radi- 

 ating furrows exist upon the anterior and posterior sections only, instead of 

 being distributed all over the scale. The upper margin of the dorsal is concave, 

 whilst it is nearly straight in A. griseus. 



D 13; A 10; C 4, 1, 8, 8, 1, 5 ; V 11 ; P 17. 

 Greyish brown above, greyish white beneath. 



Specimens of this species were collected in Milk River, affluent of the upper 

 Missouri, by Dr. George Suckley, under Gov. L L Stevens. 



The genus 



Catostomus, Lesu. 



=> 



would then be restricted to such species in which the head is moderately elon- 

 gated, the dorsal fin generally longer than high, and the size of the scales less 

 disproportionate anteriorly and posteriorly than in Acomus. The lips are papil- 

 lated and deeply cleft. The pharyngeals provided with a little expansion infe- 

 riorly. The teeth are compressed, with the inner projection of the crown alone 

 developed. 



The type of this group is Catostomus hudsonius. C. communis would be a 

 second species. And the following: 



3. Catostomus occidentalis, Ayres, Proc. Cal. Acad. Nat. Sc. i. 1854, 18. 

 Aqass. Amer. Journ. of Sc. 2d Ser. xix. 1854, 94. 



